Selective ionization of gas constituents using electrolytic reactions

ABSTRACT

An ion mobility spectrometer, ionization detector and mass spectrometer is described having a reaction region, and a region for introducing a sample gas, liquid or solid samples into the reaction region and an electrolyte in the reaction region of an alkali salt heated to a predetermined temperature, such as room temperature to 1000° C., to provide a chemical reaction between the alkali atoms, cations or complement anions with the sample to provide product ions. The invention provides a non-radioactive ionization source for ionization of a broad class of compounds.

This application is a division of application Ser. No. 701,898, filedFeb. 15, 1985 now U.S. Pat. No. 4,839,143.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a selective ionization source to be used with,for example, an ion mobility spectrometry, an ionization detector and amass spectrometry and more particularly to an electrolytic ionizationsource using inorganic/organic salts which react with sample moleculesto form product ions.

2. Description of the Prior Art

The technique of ion mobility spectrometry (IMS) was conceived in theearly 1970's in order to analyze and detect organic vapors. A typicalion mobility spectrometer (IMS) detector cell consists of a reactionregion for generating ions and a drift region for separation of ions. Inthe reaction region, reactant ions are formed using radioactivematerials such as, for example, tritium, Ni⁶³, Am²⁴¹, etc. High energyradiation from these radioactive materials ionize a carrier gas whichflows through the reaction region to form reactant ions. Coronas from amultipoint or wire array, electrons produced by photoemission andmultiphotoionization have also been proposed or used as methods toproduce ions in IMS. The ions formed through these processes are of bothpolarities and the imposed electric field determines the polarity of theions analyzed. In the absence of an electric field imposed on thereaction region, the recombination of the positive and negative ionspredominates and ion concentrations are reduced to essentially zero. Inthe presence of an electric field, ion concentrations are non-zero asthe electric field successfully competes to extract the ions from thereaction region. The nature of the reactant ions depends on thecomposition of the carrier gas. The composition of the carrier gas isselected to generate reactant ions with sufficient gas phase reactivityto allow a variety of reactions to occur between the reactant ions andsample molecules which may be introduced into the carrier gas fordetection. The types of reactions which are available for this purposeare shown by equations 1-3 for positive ions:

Proton transfer

    RH.sup.+ +M→R+MH.sup.+                              ( 1)

Charge Transfer

    R.sup.+ +M→R+M.sup.+                                ( 2)

Nucleophilic attachment

    R.sup.+ +M→MR.sup.+                                 ( 3)

Equations 4-8 show the type of reactions for negative ions:

Resonance capture

    e.sup.- (˜0.5 ev)+M→M.sup.-                   ( 4)

Dissociative capture

    e.sup.- (˜0.5 ev)+M→(M-A).sup.· +A.sup.-( 5)

Charge Transfer

    R.sup.- +M→R+M.sup.-                                ( 6)

Proton abstraction

    R.sup.- +M→RH+(M-H).sup.-                           ( 7)

Electrophilic attachment

    R.sup.- +M→RM.sup.-                                 ( 8)

In equations 1-8, R is the reactant moiety and M is the neutral samplemoiety. After the ion/molecule reactions, a mixture of reactant ions andproduct ions exists in the reaction region.

A shutter grid positioned between the reaction region and the driftregion permits momentary introduction of the ion mixture generated inthe reaction region into the drift region. This is accomplished bymomentarily removing a blocking voltage normally applied to the shuttergrid. Once in the drift region, the ion mixture drifts under theinfluence of an electric field to an ion collector, Faraday plate, in atime characteristic for each ion as measured from the shutter grid. Thedrift times for the ions and the peak amplitudes in ion current arrivingat the collector provide a basis for the identification of the chemicalspecies originally introduced into the reaction region.

The IMS technique as described above has quite a few limitations. Someof the limitations are:

1. The variety of ion/molecule reactions available for ionization usingradioactive sources does not provide specificity in the presence ofinterferences for detection,

2. Attempts to increase specificity by using non-radioactive sources,for example multiphotoionization and photoemission, results in reducedsensitivity for detection,

3. Corona discharge sources have proven to be an unreliable source ofions due to electrode sputtering processes,

4. Complex algorithms are needed to establish identification of sampleswith any present technique for providing a source of ions,

5. Sample introduction may require the use of a semipermeable membraneto eliminate effects of ambient air which is described in U.S. Pat. No.4,311,669 which issued on Jan. 19, 1982 and is assigned to the assigneeherein.

6. Use and handling of the radioactive materials must comply with U.S.Government regulations.

These limitations coupled with sensor design trade-offs, for example,sensitivity, selectivity, response time, service life, size, weight,power, etc. generally result in a compromised detection system forengineered applications.

In a publication entitled "Selective Responses Of A Flameless ThermionicDetector" by Paul L. Patterson appearing in Journal of Chromatography,167 (1978) 381-397, a flameless thermionic detector is described whichuses an electrically heated bead consisting of an alkali metal compoundembedded in a ceramic matrix. FIG. 6 shows chromatograms of a detectortest sample at two different hydrogen flow-rates. Without any hydrogen,no response was observed from azobenzene and malathion.

In U.S. Pat. No. 4,378,499, issued on Mar. 29, 1983 to G. E. Spangler,D. N. Campbell and S. Seeb and assigned to the assignee herein, an IonMobility Detector is described in which selectivity and sensitivity isenhanced. As shown in FIG. 5 of '499, a reactive coating is applied tothe internal wall of the reaction region. The reactive coating which maybe activated by heating or by radiation from an ultraviolet source isselected to provide chemical conversion of sample molecules to a moreionizable form.

In U.S. Pat. No. 3,835,328 which issued on Sept. 10, 1974 to Harris etal. and in U.S. Pat. No. 4,075,550 which issued on Feb. 21, 1978 toCastleman et al. an ionization detector was described which utilized aradioactive source to produce beta radiation to form ions from a samplegas.

In a publication entitled "Atmospheric Pressure Ionization MassSpectrometry" by D. I. Carroll et al. appearing in Applied SpectroscopyReviews, 17 (3), 337-406 (1981), a general review of atmosphericionization in mass spectrometry was provided. The use of an alkali saltwas not mentioned.

Similarly, it is also desirable to provide an ion mobility spectrometerhaving a reaction and drift region with a doped solid electrolyte in thereaction region to react with sample molecules to form product ions.

It is further desirable to generate ions in certain equipment, forexample, an ion mobility spectrometer ionization or mass spectrometerwithout the need for radioactive materials or without the need forhydrogen gas.

It is further desirable to provide an electrolytic ionization sourcewhich may be doped electrolyte where the electrolyte, such as alkalisalts, can be adjusted to undergo general or class specific reactionswith organo-phosphorous, nitrogen, and other organic or inorganiccompounds.

SUMMARY OF THE INVENTION

An apparatus for ionizing one of more constituents in a gas is describedcomprising a reaction region and drift region, an electrolyte positionedin the reaction region, an inlet for introducing the gas into thereaction region, a heater for heating the electrolyte to a predeterminedtemperature to provide an ion reaction between the electrolyte at itssurface or between electrolyte ions in the gas and selected gasconstituents to form ion products in the gas.

The invention further provides a method for generating ion products inan ion mobility spectrometer, ionization detector or mass spectrometerfrom selected sample vapors in purified gases or ambient air comprisingthe steps of heating an electrolyte, such as a salt, which may, forexample, be selected from the alkali/halogen salts (e.g. CsI, CsBr, KI,etc.), the alkali acid salts (e.g. Cs₂ SO₄, KNO₃, Li₃ PO₄, etc.), theammonium salts (e.g. NH₄ NO₃, NH₄ Cl, etc.), the alkaline earth salts(e.g. CaSO₄, BaCl₂, etc.), salts of the transition metals (e.g. AgNO₃,AgI, etc.) or complex organic salts such as salts of the carboxylic andsulfonic acids, quaternary ammonium salts, etc., or other compounds(e.g. (LaB₆) characterized by a low work function for electron emission,and mixtures thereof to a temperature in the range from room temperatureto 1000° C., dependent on the salt, passing the sample vapors in apurified or ambient air carrier gas over the electrolyte to accomplishproduct ion formation. Alternatively, in place of sample vapors, aliquid or solid may be deposited directly on the electrolyte forionization. The product ions can be formed either by reactions on thesurface of the electrolyte with subsequent evaporation into the gas fordetection or in the gas phase above or downstream from the electrolyteinvolving ion/molecule reactions with reactant ions evaporated from theelectrolyte. The invention further provides applying an electric fieldto the surface of the electrolyte to assist the movement of ions fromthe surface into the gas. The reactions may in some and do not in othersinclude the introduction of hydrogen gas into the carrier gas, however,without a flame in the reaction region.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section and schematic view of one embodiment of theinvention.

FIG. 2 is a perspective view of insulator plug 28 removed from theembodiment of FIG. 1.

FIGS. 3A and 3B are cross-section views of alternate embodiments of aportion of FIG. 2 along the lines IIIC--IIIC of FIG. 2.

FIG. 3C is a cross-section view of a portion of FIG. 2 along the linesIIIC---IIIC of FIG. 2.

FIG. 4 is a cross-section and schematic view of an alternate embodimentof the invention.

FIG. 5 is a cross-section and schematic view of an alternate embodimentof the invention.

FIG. 6 is a perspective view of insulator plug 28' removed from theembodiment of FIG. 5.

FIG. 7 is a cross-section and schematic view of an alternate embodimentof the invention.

FIG. 8 is a cross-section and schematic view of an alternate embodimentof the invention.

FIG. 9 is a cross-section view of an alternate embodiment of a solidelectrolytic source shown in FIG. 3.

FIG. 10 is a cross-section view of an alternate embodiment of a solidelectrolytic source shown in FIG. 3.

FIG. 11 is a graph showing the negative ion response of a solidelectrolytic source in the embodiment of FIG. 1 of Phosdrin vapor.

FIGS. 12-23 are graphs showing the positive ion response of a solidelectrolytic source in the embodiment of FIG. 1 to a variety of vapors.

FIGS. 24-29 are graphs showing the positive ion current from a solidelectrolytic source in the embodiment of FIG. 4.

FIGS. 30-35 are graphs showing the negative ion current from a solidelectrolytic source in the embodiment of FIG. 4.

FIG. 36 is a cross-section and schematic view of an alternate embodimentof the invention.

FIG. 37 is a cross-section and schematic view of an alternate embodimentof the invention.

FIG. 38 is a cross-section and schematic view of an alternate embodimentof the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an ion mobility spectrometer (IMS) 8 is shown foridentifying one or more constituents in a sample gas 9. A carrier gas 15with sample gas 9 passes through inlet port 11 of housing 12 intoreaction region 16. The carrier gas 15 may be, for example, a highpurity gas, such as nitrogen or purified air, as well as ambient airwith hydrogen, for example 0.1% to 2% H₂, with atmospheric hydrogen orwithout hydrogen. The atmosphere contains about 0.01% hydrogen byvolume. However, no flame is necessary in carrier gas 15, as in priorart flame detectors. Sample gas 9 may be injected into the carrier gasby means of, for example, an orifice 10 shown in FIG. 1, a syringe, amembrane inlet, an injection port, a gas chromatographic column in gaschromatography. A preconcentration device, or other suitable sampledelivery means dependent on the application may also be used.

Reaction region 16 and drift region 18 is surrounded by a plurality ofconductive rings 22 spaced apart from one another and secured into twocylindrical bodies, respectively, by a plurality of insulating rings 23.Alternatively, reaction region 16 and drift region 18 may be surroundedby two ceramic cylinders, respectively, internally coated with a thickfilm resistor as described in U.S. Pat. No. 4,390,784, which issued onJune 28, 1983 to D. R. Browning et al. and incorporated herein byreference. Reaction region 16 may be heated in the range from 23° C. to250° by resistance wires wrapped around housing 12. A high voltage biassource 25 is connected across a voltage divider 24 comprising aplurality of resistors 26 coupled in series to progressively applyincreasing voltages to the conductive rings 22 or across the resistancecoated ceramic cylinders to create a voltage gradient in the reaction 16and drift 18 regions.

A shutter grid 17 divides the reaction region 16 from the drift region18 and functions to prevent ions from entering the drift region until apulse is received from a grid pulse generator 13 over lead 14. Theshutter grid 17 may consist of a planar array of parallel wires withevery other wire in electrical contact with each other and to lead 14.Alternatively, the shutter grid may be a parallel plane shutter gridconsisting of two grids displaced from each other along the axis 27 ofthe IMS cell 8. The other wires are coupled together and to lead 19.When the grid pulse generator 13 provides a first voltage to lead 14,ions generated in reaction region 16 are collected by the grid wires 17and are not allowed to enter drift region 18. When the grid pulsegenerator 13 momentarily provides a second voltage to lead 14, ionsgenerated in reaction region 16 are allowed to enter drift region 18without being collected by grid wires 17. The grid pulse generator 13 isreferenced to the voltage divider circuit 24 by means of lead 19 and isisolated from low voltage control circuitry, for example, byoptoisolators. Grid pulse generator 13 may be free running or mayreceive a control signal over lead 20.

Inserted into the first conductive ring 21 of reaction region 16 is aninsulator plug 28 with an outside diameter less than the inside diameterof conductive ring 21. Insulator plug 28 is constructed of a materialwith high temperature compatibility, for example, boron nitride,ceramic, alumina, glass or MACOR. MACOR is a machinable ceramic, such asdescribed on a 1974 Technical Data Sheet AX-3000 from Duramic Products,Inc. of Pallisades Park, N.J. The space between insulator plug 28 andconductive ring 21 allows carrier gas 15 with sample gas 9 to flow intoreaction region 16. Insulator plug 28 is held in position by two O-rings29 and 30.

Through insulator plug 28 are two spaced apart 0.127 cm (0.050 inch)terminal leads 31 and 32 to which is attached a 0.0254 cm (0.010 inch)90% Tungston/10% Iridium, or other suitable metal, heater filament 33.Heater filament 33 is coated with an electrolyte 34. The surface 35 ofthe electrolyte 34 is heated by heater filament 33, which is coupled toheater supply 36 over leads 31 and 32. Heater filament 33 andelectrolyte 34 is positioned in reaction region 16 to permit directimpingement of sample gas molecules 9 thereon to assure surfaceionization of sample gas molecules 9 at surface 35. Heater supply 36 isisolated from ground potential through transformer 37. Transformer 37has a first winding coupled over leads 38 and 39 to a source of powerand a second winding coupled over leads 40 and 41 to heater supply 36.Lead 41 is also coupled to high voltage bias source 25 to allow theelectrolytic source 34 to float at voltage V_(R), the voltage appliedover lead 42 to conductive ring 21, or above V_(R) by a voltage V_(s) inthe range from 0 to 3000 volts. Electrolytic source 34 will have themost negative or positive voltage of the IMS cell, depending on thepolarity selected for the high voltage bias source 25.

The surface temperature of electrolytic source 34 is heated without aflame or combustion to a predetermined temperature in the range fromroom temperature to 1000° C., depending on the electrolyte and theelectric field applied to surface 35 of electrolytic source 34. Theelectrolytic source 34 functions to react with sample molecules 9 at orin contact with surface 35 to produce positive or negative product ions44. Or, electrolytic source 34 functions to evaporate from surface 35into the gas phase in reaction region 16 to react with sample molecules9 to produce positive or negative product ions 44. Product ions 44,dependent upon the polarity of V_(R), travel in the direction of thearrow 45 but are prevented from entering drift region 18 by shutter grid17.

Periodically, shutter grid 17 is momentarily biased by a voltage pulseon lead 14 to allow conduction of product ions 44 into the drift region18. Within drift region 18, product ions 44 move or accelerate towardscollector 46 as shown by arrow 47. A stream of non-reactant drift gas 48is injected into port 49 and passes through drift region 18, as shown byarrows 50-52. Drift gas 48 is exhausted through ports 53-55, as shown byarrows 56-58. Product ions 44 of different molecules attain differentterminal velocities, inversely related to their collision cross section(mass), so that the presence of molecules of a constituent gas in aparticular sample can be determined by sampling the detector output onlead 59 at predetermined times delayed from the initial gating pulseapplied to shutter grid 17. When the product ions 44 reach collector 46,positive or negative charge is collected by collector 46 and carriedover lead 60 to an input of electrometer detector 61 which amplifies andmeasures the current received by collector 46. Collector 46 as describedhere is also a Faraday plate. Detector 61 may, for example, include anoperational amplifier 62 having a resistor 63 coupled between its inputon lead 60 and its output on lead 59. A second input to amplifier 62 maybe coupled to ground.

The output of grid pulse generator 13 is coupled over lead 14 to aninput of clock 64 which measures the time elapsed since the last triggerpulse and provides a proportional signal on lead 65. When this lapsetime on lead 65 is correlated with the appearance of maxima in ioncurrent as sensed by the electrometer detector 61, the time for variousions to drift through drift region 18 can be measured. Alternatively,the ion mobility spectrum (display including all peaks) can be takenwith an oscilloscope or similar equipment. The inverse of the lapse timeis a measure of the mobility of the ions.

Aperture grid 66 is biased above ground by resistor 67. Resistor 67 iscoupled between ground and lead 68. Capacitor 69 is also coupled betweenground and lead 68. Aperture grid 66 shields collector 46 from effectsof induced charge as the product ions 44 travel the length of driftregion 18 before passing through aperture grid 66 to collector 46.

FIG. 2 shows a perspective view of insulator plug 28 and electrolyticsource 34 after removal from the embodiment of FIG. 1. Leads 31 and 32pass through insulator block 28 where they are attached to heaterfilament 33 shown protruding from the end of insulator plug 28. As shownin FIG. 2, a thin coat of electrolyte 34 is applied to heater filament33. When insulator plug 28 is inserted into the opening in housing 12fitted by O-rings 29 and 30, electrolytic source 34 is positioned asshown in FIG. 1 inside conductive ring 21 and serves as a source ofions. In addition to the ability of introducing sample gas 9 throughport 11, insulator plug 28 may be removed from the embodiment of FIG. 1and heater filament 33 used to collect sample molecules either as apreconcentrator which adsorbs molecules from a gas or as a result ofapplying liquid solutions to heater filament 33 or electrolyte 34. Inthis way, salts, electrolytes, and solutions of these with samplemolecules can be analyzed when insulator plug 28 is reinserted into theion mobility spectrometer 8 shown in FIG. 1 and the heater filament 33may be, for example heated rapidly (flashed) by heater supply 36. Thedirect application of sample molecules to heater filament 33 and solidelectrolytic source 34, as described above, is very useful for analyzingvolatile electrolytes and salts, as well as liquids.

FIGS. 3A and 3B are cross-section views of alternate embodiments of apart of FIG. 2. FIG. 3C is a cross-section view of a part of FIG. 2along the lines IIIC--IIIC. In FIGS. 3A-3C, heater filament 33 which maybe a portion of leads 31 and 32 may, for example, be composed ofNICHROME, platinum, iridium, rhodium or other suitable metals ormaterials for resistance heating. Generally, platinum (particularly 10%iridium in platinum) is more resistant to corrosion by electrolytes.

In FIG. 3A, electrolyte 34 forms a layer on heater filament 33.Electrolyte 34 may have thickness, for example, of .025 millimeters(.001 inches) shown by dimension t.

In FIG. 3B, electrolyte and cement forms a layer 34' on heater filament33. Layer 34' may have a thickness, for example 0.64 centimeters (0.25inches), shown by dimension d.

In FIG. 3C, heater filament 33 may be protected from corrosion by aninert layer 72, for example quartz formed from decomposition of OV-275,glass, cement without electrolyte, or cement without electrolytecontaining zinc oxide. Inert layer 72 may be, for example, a thincoating on heater filament 33 in the range from 0 to 0.60 cm thick. Forthicker coatings the heater filament 33 must be completely coated withthe film to avoid development of hot spots in the filament which canlead to burn-out. Inert layer 72 either provides a barrier to themigration of the electrolyte 34 to heater filament 33 or inert layer 72with zinc oxide reacts with electrolyte 34 and neutralizes it. Finally,it is advisable to provide inert layer 72 over the entire heaterfilament 33 to prevent neutral molecules of the electrolyte in eithersolid liquid or gas form from reaching heater filament 33, and corrodingthe heater filament 33. This provides a longer life heater filament 33.

The electrolytic source 34 is preferably a composition formed by firingan electrolyte into an alumino-silicate mixture or impregnating a glassmatrix with electrolyte. The electrolytic source 34 may be coated overheater filament 33 and over inert layer 72, if provided, to form a beador coating such that the thickness of the electrolyte is reasonablyuniform around the heater filament 33, which may be preformed to assuremaintenance of a uniform temperature on the surface of the coating ofthe electrolytic source 34.

As shown in FIG. 3C, heater filament 33, along with leads 31 and 32, maybe cylindrical in shape with electrolytic source 34 forming a layer,sleeve or cylinder over heater filament 33 and inert layer 72 having athickness D as shown by arrow 73 from surface 35 to inert layer 72.

FIG. 4 is a cross-section and schematic view of an alternate embodimentof the invention. In FIG. 4, like references are used for functionscorresponding to the apparatus of FIG. 1. In FIG. 4, conductive ring 75contains a grid 76 which extends across the end of conductive ring 75,which is also the diameter of reaction region 16. Grid 76 may be formedby conductive wires strung across one end of conductive ring 75. Thewires may be positioned parallel to one another. Alternatively, thewires may cross one another forming a mesh. Grid 76 is positioned inclose proximity to electrolytic source 34. Alternatively, theelectrolytic source 34 may be positioned in close proximity to grid 76having a spacing in the range from 0.01 to 1 cm. Depending upon thediameter of the electrolytic source 34 and the spacing from grid 76depending on the potential V_(s) supplied to electrolytic source 34,relative to the potential of grid 76, high electric field strength canbe applied to the surface 35 of electrolyte 34. The electric field onsurface 35 may be enhanced by 1/r by using a smaller diameter source 34where r is the radius of source 34. The voltage V_(s) of heater filament33 may be in the range from 0 to 3000 v, for example 2000 v, withrespect to the voltage of grid 76. By inserting grid 76 in reactionregion 16 in close proximity of solid electrolytic source 34, themagnitude of the field strength applied to the surface 35 ofelectrolytic source 34 may be increased by 10² to 10⁴ compared to thefield strengths without grid 76. The electric field strength may beselected in a range below an electric field strength which would causearcing between heater filament 33 and grid 76. Susceptibility to arcingwill be dependent on the internal pressure selected in reaction region16. In normal operation, the pressure internal to the ion mobilityspectrometer 8 is typically 1 atmosphere.

In operation of the embodiment of FIG. 4, heater filament 33 is heatedto a predetermined temperature. In addition, the voltage V_(s) of heaterfilament 33, relative to grid 76, is applied to provide a strongelectric field at surface 35 of the electrolytic source 34. The electricfield at surface 35 facilitates ion evaporation from the electrolyticsource 34. The temperature and electric field at surface 35 may beadjusted to optimize ion evaporation, while limiting neutral moleculeevaporation from the electrolytic source 34. The electric field atsurface 35 helps to pull ions off surface 35 into the carrier gas 15 andsample gas 9 in reaction region 16. While pulling ions off surface 35,gas phase reactions for positive ions may occur such as described byequation (3). One example of a suitable reactant ion in equation (3) iscesium or other alkali metal cations. The apparatus shown in FIG. 4 isalso suitable for producing negative ions which may then be used toprovide a gas phase reaction described by equations (6) and (8). Inequations (6) and (8) one example of a suitable reactant ion may beiodine or other halogen anions. It is further understood in theembodiment of FIG. 4 that surface ionization may also occur when gasmolecules in reaction region 16 impinge upon surface 35 in accordancewith equation (9): ##STR1## It is noted that surface ionization requirescontact between the sample molecule and the thermally excited atoms onsurface 35.

In the embodiment of FIG. 4 the voltage V_(D) may be 600 v, the voltageVR may be 270 v, and the voltage V_(s) may be 2000 v above the voltageV_(R). The voltages V_(D), V_(R) and V_(s) are of the same polaritywhich would be positive for positive ions and negative for negativeions. In FIG. 4 the distance between electrolytic source 34 and shuttergrid 17 may be, for example, 2 cm and the distance between shutter grid17 and collector 46 may be, for example, 4 cm. The spacing betweenelectrolytic source 34 and grid 76 may be, for example, in the rangefrom 0.01 to 1 cm. Grid 76 may be formed from wires having a diameter inthe range from 100 micron to 0.20 cm. The spacing between parallel wiresmay be, for example, in the range from 100 micron to 1.5 cm.

FIG. 5 shows a cross-section and schematic view of ion mobilityspectrometer 8". In FIG. 5 like references are used for functionscorresponding to the apparatus of FIG. 4. In FIG. 5 carrier gas 15 flowsthrough tube 80 to insulator plug 28'. A passageway 81 passes throughthe center of insulator plug 28' to permit carrier gas 15 and sample gas9 to impinge upon electrolytic source 34. Passageway 81 may be formed ininsulator plug 28' at the time it is made or subsequently provided ininsulator 28' as needed. The arrangement shown in FIG. 5 with passageway81 through insulator plug 28' facilitates the process of surfaceionization by impinging carrier gas 15 and sample gas 9 on surface 35 ofelectrolytic source 34.

FIG. 6 is a perspective view of insulator plug 28' removed from theembodiment of FIG. 5. In FIG. 6 passageway 81 is shown extending fromone end to the other of insulator plug 28'. The passageway may be formedby drilling to provide clearance for a Teflon tube insert, where thematerial for insulator 28, is MACOR, previously referred to herein.

FIG. 7 is a cross-section and schematic view of ion mobilityspectrometer 8'". In FIG. 7 like references are used for functioncorresponding to the apparatus of FIG. 5. In FIG. 6 insulator plug 28'is modified to hold a reservoir 79 of electrolyte 34 interior ofpassageway 81, which has been enlarged at the end of insulator plug 28".The electrolytic source 34 may, for example, be in the shape of a hollowcylinder to permit carrier gas 15 and sample gas 9 to pass therethroughand to impinge on heater filament 33. As shown in FIG. 7 a quantity ofelectrolytic source 34 may be deposited interior of passageway 81, whichfunctions as a reservoir 79 by holding a large quantity of electrolyte34 to extend the life of the electrolyte 34. The interior surface 35' ofthe electrolytic source 34 is in direct contact with the gases passingthrough passageway 81. A heater coil 83 may be positioned at the end ofinsulator plug 28" to heat the electrolyte 34 to a predeterminedtemperature. Power to heater coil 83 may be supplied by lead 84 which iscoupled to lead 31 and by lead 85 which is coupled to heater supply 36'.Heater supply 36' functions to provide power to heater coil 83independent of the power supplied to heater filament 33.

FIG. 8 is a cross-section and schematic view of ion mobilityspectrometer 88. In FIG. 8 like references are used for functionscorresponding to the apparatus of FIG. 1. Carrier gas 15 flows down tube89 as shown by arrow 90 to junction 91, wherein carrier gas 15 isdivided into two streams. One stream flows through tube 92 into inletport 11, as shown by arrow 93. The second stream flows through tube 94into passageway 81, as shown by arrow 95. Tube 94 has an orifice or pinhole 10' for introducing sample gas 9 into carrier gas 15 flowingthrough tube 94. Sample gas 9 may also be introduced into tube 94 from amembrane inlet, injection port, gas chromatographic column, diffusionmembrane inlet or other suitable means dependent on the application.

In operation, carrier gas 15 is divided, for example by a valve orvalves, such that only 1% to 100% of carrier gas 15 in tube 89 flowsthrough tube 94. The carrier gas 15 in tube 94 receives sample gas 9through orifice 10' and passes through passageway 81 in insulator plug28'. Carrier gas 15 and sample gas 9 exit passageway 81 and flow oversurface 35 of solid electrolyte 34. Electrolyte 34 has been positionedin the path of carrier gas 15 and sample gas 9 at the outlet ofinsulator plug 28'. By reducing the carrier gas 15 flowing passedsurface 35 of electrolyte 34, the reaction probability of sample gas 9is maximized without inducing large flows of carrier gas 15 aroundsurface 35 which tends to cool surface 35, resulting in heat losses fromelectrolyte 34. The remaining carrier gas 15 passes through tube 92 intoreaction region 16 without flowing over surface 35. For example, carriergas 15 in tube 92 may be introduced in reaction region 16 such that thegas mingles with the sample gas and ions down stream from theelectrolytic source 34 to facilitate the purity of the normalenvironment of the reaction region 16, as shown by arrows 96 and 97.Arrow 98 shows the flow of carrier gas 15 and sample gas 9 passed theelectrolytic source 34 prior to mixing with carrier gas 15 downstreamfrom the position of arrows 96 and 97 which had flowed through tube 92.In FIG. 8 tubes 89, 92 and 94 may be constructed from materialsincluding tetrafluoroethylene, stainless steel or glass. Passageway 81may be enlarged to allow a portion of tube 94 to be inserted throughpassageway 81 into reaction region 16 or merely to the end of insulatorplug 28'.

FIG. 9 is a cross-section view of an alternate embodiment of anelectrolytic source 34 shown in FIG. 3. In FIG. 9 like references areused for functions corresponding to the apparatus of FIG. 3. In FIG. 9an inert layer 72' is applied to heater filament 33, which functions toprotect heater filament 33 from chemical attack and to hold solidelectrolyte 34 in grooves or pores 102 in inert layer 72'. Theindentations, grooves or pores 102 function to hold electrolyte 34 inexcess quantities to extend the life of the electrolytic source 34.Grooves or pores 102 with solid electrolytic source 34 form a reservoirfrom which the rate of evaporation of electrolyte 34 may be controlled.Inert layer 72' may have a uniform thickness from the surface of heaterfilament 33 and the outer surface of inert layer 72', as shown by arrow104. The outer surface 103 of inert layer 72' between grooves or pores102 essentially reduces the surface area of electrolyte 34 compared witha completely coated surface as shown in FIGS. 3A-3C. Grooves or pores102 may extend in inert layer 72' around heater filament 33 in the formof rings, a continuous thread or voids. Alternately, grooves or pores102 may be microscopic indentations as might be provided by microporousceramic and sieve materials or by foam metals. Grooves or pores 102 mayhave a width shown by arrow 106 in the range from 3 angstroms to 0.16cm. Heater filament 33 may also be in the form of a coil, helix orspiral, as well as an arc or part of a polygon between leads 31 and 32.

FIG. 10 is a cross-section view of an alternate embodiment of a solidelectrolytic source 34. A tube 110 which may be, for example, porous andmade of ceramic or other suitable material is filled with electrolyte111. Ends 112 and 113 of tube 110 may be opened or sealed, dependingupon the electrolyte. Tube 110 may have holes 114 which are spaced apartand which may have a diameter in the range from 25 to 1000 microns shownby arrow 115. Holes 114 expose a portion of the surface 116 of solidelectrolyte 111 to allow its evaporation rate to be controlled. A heaterfilament 117 having a protective coating 118 is wrapped around tube 110and functions to heat tube 110 and solid electrolyte 111 to apredetermined temperature. Heater filament 117 is coupled to leads 31and 32. Protective coating 118 may be formed by heating heater filament117 to a temperature below the flash point of a silicon grease, such asin the range from 300° to 500° C. One example of a silicon greasesuitable to form a coating is dicyanoallyl silicone identified as OV-275and listed as Item no. 08251 by Applied Science located in Deerfield,Illinois. When OV-275 is applied to heater filament 117, it decomposesand rearranges itself to leave behind a thin layer of quartz (SiO₂) onthe surface of heater filament 117. The other decomposition productsresulting from the process can be removed with a solvent such aschloroform. The solid electrolytic sources as shown in FIGS. 9 and 10are suitable for operation in the embodiments of FIG. 1, 4, 5 and 8.

The electrolytic sources as shown in FIGS. 3A, 9 and 10 provide animprovement on a cement impregnated electrolytic source shown in FIGS.3B and 3C, since a cement impregnated solid electrolytic source due toits bulk requires excessive power to heat the source (6 to 7 watts), itsinitial operation causes excessive amounts of salt to evaporate and coatthe internal surfaces of insulating rings 23, of the ion mobilityspectrometer causing shorts to develop within the cell, particularly athigh temperature, and gives rise to peculiar flow rate dependentcharacteristics. Furthermore, sources based on impregnated cementprovide no negative ion response in the ion mobility spectrometer, theelectrolyte melts causing electricity to flow through the electrolyterather than the heater filament, and the ion current obtained from thesource goes through a maximum as the source temperature is increased.Therefore, the cement impregnated source has become less attractive asthe preferred approach to the design of an electrolytic source.Impregnated ceramic, glass or alumino-silicate sources offer advantagesin purity of materials which can be used to construct the source and asimple coat of electrolyte on a heater filament provides simplicity ofdesign.

FIG. 11 is a graph showing the negative ion response of the embodimentof FIG. 1. An electrolytic source 34 of Dylon-ClO cement impregnatedwith either cesium bromide (CsBr) or rubidium sulphate (Rb₂ SO₄) wasused with similar results. The electrolytic source 34 was baked severalweeks at low power to remove impurities from the cement. Without baking,a response was observed from phosdrin but was masked by interferingimpurity peaks. In FIG. 11 the ordinate represents negative ion currentand the abscissa represents ion drift time. Phosdrin was introduced intoa purified air carrier gas 15 containing no hydrogen and flowed pastelectrolytic source 34 which was heated. Curve 121 shows a negative ioncurrent at the output of detector 61 occurring at about 12.8 ms. In FIG.11, the response to phosdrin is believed to be due to the surfacereaction shown by equation (10): ##STR2## where A^(*) is a thermallyexcited alkali metal atom, rubidium, M is the sample molecule, phosdrin,A⁺ is the ionized alkali cation and M⁻ is the ionized sample molecule ora fragmemt thereof. The surface reaction of equation (10) is believed tooccur because of the low ionization potential of the alkali metals, suchas cesium and rubidium. However, the reactions to produce negative ionsmay also be electrochemical, catalytic, thermionic, dissociative, etc.or any combination thereof. The response as shown in FIG. 11 graduallydisappeared after several weeks of continuous operation, but could beregained by recoating the heater filament 33 with additionalelectrolytic source 34.

FIGS. 12-23 are graphs showing the positive ion response of anelectrolytic source 34 in the embodiment of FIG. 5 without grid 76 to avariety of vapors. In FIGS. 12-23 the ordinate represents positive ioncurrent and the abscissa represents ion drift time. An electrolyticsource 34 of rubidium nitrate mixed with Sauereisen cement 29 was usedas shown in FIG. 3B to obtain the graphs for FIGS. 12-23. The cementused was Sauereisen 29 cement, available from Sauereiesn Cement Co.,Pittsburgh, Pa. The electrolytic source 34 was baked for several weeksto remove impurities from the cement. With rubidium nitrate as theelectrolytic source 34, alkali cations, rubidium, was observed from thesource as reactive ions (FIG. 12) which undergo attachment reactionswith sample molecules (FIGS. 13-23). The gas phase reaction is shown inequation (11):

    A.sup.+ +M→MA.sup.+                                 (11)

In equation (11) A⁺ is the alkali cation, rubidium, M is the samplemolecule, and MA⁺ is the attached complex.

In FIG. 12, curve 122 shows the positive ion current of reactant ions,rubidium from electrolytic source 34 in FIG. 1. Curve 122 was obtainedwhile a carrier gas was introduced into reaction region 16, but with nosample gas 9. Curve 123 in FIG. 13 shows the response where sample gas 9is ammonium hydroxide. Peak 124 is from the rubidium reactant cation.Unlike the strong response obtained from NH₄ OH using a conventionalradioactive source for IMS, essentially no response is observed forammonium hydroxide other than the alkali reactant cation. Curve 125, inFIG. 14, shows the response where sample gas 9 is acetone. A product ionis observed for acetone. Curve 126 in FIG. 15 shows the response wheresample gas 9 is benzene. Peak 127 is from the rubidium reactant cationand hence no product ions are observed for benzene. Curve 128 in FIG. 16shows the response where the sample gas 9 is xylene. Peak 129 is due tothe rubidium cation and no product ions from xylene are observed. Curve130 in FIG. 17 is a response from ion mobility spectrometer 8 where thesample gas 9 is ethanol. Peak 131 is due to the rubidium cation and theother peaks are product ions. Curve 132, in FIG. 18, is a response wherethe sample gas 9 is dimethylformamide. Peak 133 is due to the rubidiumcation. Curve 134, in FIG. 19, is the response due to 3-Hexanone. Peak135 is due to rubidium. Curve 136 in FIG. 20 is a response due tocyclohexanone. This is a saturated response where the rubidium cation isused up in the reaction. Curve 138 in FIG. 21 is a response due tophosdrin. Peak 139 is due to the rubidium cation. Curve 140 in FIG. 22is a response due to the chemical DMMP. Curve 142 in FIG. 23 is aresponse due to the chemical DIMP. Attachment reactions as shown byequation (11) were verified by differences in mobilities of observedproduct ions obtained from proton attachment reactions in the presenceof a radioactive source and alkali attachment reactions in the presenceof the alkali cation. By using an electrolytic source, the ammonium ionwas not observed as shown in FIG. 13. When using a radioactive source inan ion mobility spectrometer, ammonium hydroxide is ionized with theformation of an ammonium ion. Further, by using a cement impregnatedsource, no negative ions were observed from a source of alkali saltwhich was contrary to expectations.

FIGS. 24-29 are graphs showing the positive ion current from anelectrolytic source which is coated directly on heater filament 33 asshown in FIG. 3A in the embodiment of FIG. 5 without grid 76. In FIGS.24-29 the ordinate represents positive ion current and the abscissarepresents time. To obtain the data in FIGS. 24-29 heater filament 33was coated with an electrolyte by depositing water solutions ofelectrolyte on an incandescent wire. No cement was used. The heater wire33 along with insulator plug 28' was then inserted into reaction region16 of ion mobility spectrometer 8" as shown in FIG. 5. In FIG. 24 curve146 shows the positive ion current observed when lithium chloride (LiCl)was used as the electrolyte. In FIG. 25 curve 147 shows the positive ioncurrent from potassium fluoride (KF). In FIG. 26 curve 148 shows aresponse from sodium chloride (NaCl). In FIG. 27 curve 149 shows apositive ion current from an electrolytic source of cesium bromide(CsBr). In FIG. 28 curve 150 shows a positive ion current from anelectrolytic source of rubidium sulfate (Rb₂ SO₄). In FIG. 29 curve 151shows the positive ion current observed from an electrolytic source ofammonium nitrate (NH₄ NO₃). In all cases a positive reactant ion isobserved which came off the electrolytic source and could support gasphase reactions such as shown by equations (12) and (13).

    M+R.sup.+ →MR.sup.+                                 (12)

    M+R.sup.+ →M.sup.+ +R                               (13)

In equations (12) and (13) M is the sample molecule and R⁺ is thereactant ion. The reactant ion would be the alkali cation in FIGS. 24-28and the ammonium ion would be the reactant ion in FIG. 29.

FIGS. 30-35 are graphs showing the negative ion current from a solidelectrolytic source in the embodiment of FIG. 5 without grid 76. InFIGS. 30-35 the ordinate represents negative ion current and theabscissa represents ion drift time. Heater filament 33 was coated bydepositing water solutions of electrolyte on an incandescent wire. Aftercoating, the insulator plug 28 was reinserted into reaction region 16 ofion mobility spectrometer 8'. In FIG. 30, curve 156 shows the negativeion response from an electrolytic source of sodium fluoride (NaF). InFIG. 31 curve 157 shows the negative ion current from a solidelectrolytic source of sodium bromide (NaBr). In FIG. 32, curve 158shows the negative ion current from an electrolytic source of potassiumiodide (KI). In FIG. 33 curve 159 shows the negative ion current from anelectrolytic source of cesium sulfate (Cs₂ SO₄). In FIG. 34, curve 162shows a negative ion current from an electrolytic source of KH₂ PO₄. InFIG. 35 curve 164 shows a negative ion current from an electrolyticsource of K₂ HPO₄. FIGS. 30-35 show that negative reactant ions areavailable from an electrolytic source using alkali halide salts tosupport gas phase reactions with asample gas. These reactions are givenby equations (14) and (15) as

    M+R.sup.- →M.sup.· R.sup.-                 (14)

    M+R.sup.- →M.sup.- +R                               (15)

In equations (14) and (15) M is the sample molecule and R⁻ is thereactive ion. It is noted that multiple negative ions are available fromthe sulfates, nitrates and phosphates which may complicate ion/ moleculereaction chemistries for these salts. The reactant ions generated ineach case are not all expected to be the same even though drift timesare similar. Different ion/molecule reaction chemistries may be observedin each case. A consequence of this consideration is that the chemistryused for ionization can be varied and adjusted to the sample by varyingthe alkali source composition. In collecting the data of FIGS. 24-35, itwas found that the positive or negative ion current detected depended onthe temperature of heater filament 33, the electric field applied to theheater filament, and the salt used for the electrolytic source. Forexample, the ammonium ion from the ammonium salt could be generated atvery low source heater powers when compared to other salts. Lower heaterpowers were also required to generate ions from CsI than from the otheralkali/halide salts.

In the embodiment of FIG. 1, carrier gas 15 and drift gas 48 are shownexiting ports 53-55. An alternate arrangement for operation of ionmobility spectrometer 8 would be to introduce carrier gas 15 at ports 53and 54 with the drift gas 48 and carrier gas 15 flowing through reactionregion 16 in the opposite direction shown by arrow 45 and out throughinlet port 11 to the exterior of housing 12. Another alternateembodiment would be to introduce drift gas 48 at ports 53 and 54 whichwould flow through drift region 18 along with carrier gas 15 and exitout port 49. Another alternate embodiment would be to seal up ports 53and 54 and allow carrier gas 15 to flow through drift region 18 and outport 49 with drift gas 48 disconnected. The latter two alternateembodiments appear the least desirable. One reason for using the firstalternate approach with the carrier gas 15 and drift gas 48 exiting port11 is to prevent condensation of electrolyte 34 on conducting rings 22,insulating rings 23 and shutter grid 17. Condensed vapors of electrolyteon the interior walls of regions 16 and 18 tend to short-out or distortthe electric field within regions 16 and 18. In addition, drift gasflowing through the reactor decreases the response time of theinstrument as might be required when it is coupled to a gaschromatograph.

Referring to FIG. 36, an ionization detector 210 is shown. In FIG. 36,like references are used for functions corresponding to the apparatus ofFIG. 5. A sample gas 9, which may include carrier gas 15, enters housing12 at port 11 and passes over electrolytic source 34. Sample gas 9 maycontact surface 35 or react with electrolytic ions 213 in the gas phase.Grid 76 provides an increased electric field at surface 35 by way ofheater supply 36 potential V_(g) over line 229. Sample gas 9 is ionizedby electrolytic source 34 at surface 35 or in the gas phase to form ions211. Ions 211 pass through grid 212 along a channel or path 214 betweenbaffles 215-220, shown by arrows 221-226. Baffles 215-220 function tolenghten the path of ions 211 between electrolytic source 34 andcollector 46. Grid 231 which may, by a plurality of wires or a screenand voltage supply 232, provide an electric field between grid 231 andcollector 46 to move ions 211 to collector 46. Collector 46 is nearground potential by way of the virtual ground input of electrometerdetector 61. It is understood that negative ions 211 may also be formedby electrolytic source 34. Ions 211 are collected by collector 46 arecoupled to electrometer detector 61 which provides an output on lead 59.Insulators 227 and 228 function to insulate and support collector 46with respect to housing 12. The electrolytic source 34 may be used incombination with a radioactive source 230 which may be, for example,incorporated in grid 212. For a further description of an ionizationdetector, reference is made to U.S. Pat. No. 3,835,328 which issued onSept. 10, 1974 and to U.S. Pat. No. 4,075,550 which issued on Feb. 21,1978 which are incorporated herein by reference.

Referring to FIG. 37, a mass spectrometer 240 is shown. In FIG. 37 likereferences are used for functions corresponding to the apparatus ofFIGS. 1 and 36. A sample gas 9 which may include carrier gas 15 entershousing 12 at port 11 by way of, for example, pin hole 249 and passesover electrolytic source 34. Ions 211 which may be positive or negativepass through opening 242 through electrostatic lenses 243. When ions 211enter region 250, they travel as shown by arrow 246. During theirresidence in region 250, the ions 211 are mass separated by means of amagnetic field (magnetic-sector mass spectrometers), cross RF and DCfields (quadrupole mass spectrometer), or other conventional means forseparating ions according to charge/mass ratios. Elements 244 and 245 ofFIG. 37 are two of four rods typically used in the construction of aquadrupole mass spectrometer. After ions 211 are mass analyzed, theyarrive at collector 247 which may be either a Faraday plate, achanneltron (shown in FIG. 37) or an electron multiplier. An outputcurrent is coupled over lead 252. The pressure maintained within housing12 is in the range from 10⁻⁵ Torr to 10⁻⁹ Torr by pump 254. Pin hole(e.g. 20 micron diameter) 249 can be used to couple sample gas 9 atatmospheric pressure to the reduced pressure conditions of massspectrometer 240. Other means for introducing sample gas 9 may be amembrane inlet, by a gas chromatograph inlet, by direct deposition onsource 34 which is a part of a standard solids probe, etc. Electrolytesource 34 may be used in combination with other source of ions forexample electron impact, chemical ionization, field ionization, etc.

Referring to FIG. 38 a mass spectrometer 260 is shown. In FIG. 38, likereferences are used for functions corresponding to the apparatus of FIG.37. A sample gas 9 which may include carrier gas 15 enters housing 12 atport 11 at or near atmospheric pressure and passes over electrolytesource 34. Sample gas 9 may contact surface 35 or react withelectrolytic ions 213 in the gas phase. Grid 76 provides an increasedelectric field at surface 35 by way of heater supply 36 potential V_(g)over line 229. Sample gas 9 is ionized by electrolytic source 34 atsurface 35 or in the gas phase by electrolytic ions 213 to form ions211. Sample gas 9 exits port 263 shown by arrow 264. Ions 211 which maybe positive or negative pass through inlet or pin hole 262 throughelectrostatic lenses 243. Voltage source 248 may apply a bias voltage tothe plate 259 having pin hole 262. The ions are mass separated, forexample, by a quadrupole mass spectrometer. Elements 244 and 245 are twoof four rods typically used in the construction of quadrupole massspectrometer 260. After ions 211 are mass analyzed, the separated ionsarrive at collector 247 which may be either a Faraday plate, achanneltron shown in FIG. 38 or an electron multiplier. An outputcurrent is coupled over lead 252. The pressure in the region ofelectrostatic lens 243, elements 244 and 245 and collector 246 ismaintained in the range from 10⁻⁵ to 10⁻⁹ Torr by pump 254 and housing266. Housing 12 is coupled to housing 266 by inlet or pin hole 262.

The invention describes an ion mobility spectrometer or detector foridentifying one or more constituents in a gas comprising means forintroducing the gas into a reaction region, an electrolyte such as analkali salt which may, for example, include rubidium sulfate or cesiumiodide positioned in the reaction region having a surface exposed to thegas, a heating element for heating the electrolyte to a predeterminedtemperature to provide an ion reaction between the electrolyte andselected constituents in the gas to form ion products in the gas,electrodes for providing an electric field inside the housing across theion products to move the ion products away from the electrolyte surface,and further electrodes for measuring the drift mobility and quantity ofthe ion products, whereby the presence of certain ion products may beindicated.

The invention further provides a method for generating ion products inan ion mobility spectrometer, ionization detector, and mass spectrometerfrom gas constituents or trace compounds in an ambient gas comprisingthe steps of heating an electrolyte, for example, an alkali salt to apredetermined temperature and passing the ambient gas over theelectrolyte, whereby an ion reaction with the constituent gas generatesthe ion products. The invention provides highly sensitive, chemicalclass and compound specific detection of trace gases and compounds.

The invention claimed is:
 1. A method for generating product ions fromsample molecules in an ion mobility spectrometer, comprising the stepsof:positioning an electrolytic ionization source consisting essentiallyof an electrolyte in a reaction region; heating said electrolyte togenerate reactant cations; using an electric field to assist in theextraction of the reactant cations into the gas phase; transporting saidsample molecules in a carrier gas to said reaction region to be mixedwith the reactant cations, causing ion-molecule reactions between saidsample molecules and reactant cations in the gas phase, saidion-molecule reactions occurring proximate to and at a distance fromsaid electrolyte; whereby said ion-molecule reactions produce productions independently of said carrier gas composition and without a needfor hydrogen to catalyze said ion-molecule reactions; and submittingsaid product ions to a drift tube of said ion mobility spectrometer forseparation of said reactant cations from said product ions, and forseparation of said product ions which have different mobilities.
 2. Themethod according to claim 1, wherein said electrolyte is a solidelectrolyte.
 3. The method according to claim 2, wherein said solidelectrolyte is coated on a heating element.
 4. The method according toclaim 3, wherein said heating element is a filament.
 5. The methodaccording to claim 2, wherein a heating element is embedded in saidsolid electrolyte.
 6. The method according to claim 5, wherein saidheating element is a filament.
 7. The method according to claim 1,wherein said electrolyte is a salt.
 8. The method according to claim 7,wherein said salt is coated on a heating element.
 9. The methodaccording to claim 8, wherein said heating element is a filament.
 10. Amethod for generating product ions from sample molecules in an ionmobility spectrometer, comprising the steps of:positioning anelectrolytic ionization source consisting essentially of an electrolytein a reaction region; heating said electrolyte to generate reactantanions; using an electric field to assist in the extraction of thereactant anions in the gas phase; transporting said sample molecules ina carrier gas to said reaction region to be mixed with the reactantanions, thereby causing ion-molecule reactions between said samplemolecules and reactant anions in the gas phase, said ion-moleculereactions occurring proximate to and at a distance from saidelectrolyte; whereby said ion-molecule reactions produce product ionsindependently of said carrier gas composition and without a need forhydrogen to catalyze said ion-molecule reactions; and submitting saidproduct ions to a drift tube of said ion mobility spectrometer forseparation of said reactant anions from said product ions, and forseparation of said product ions which have different mobilities.
 11. Themethod according to claim 10, wherein said electrolyte is a solidelectrolyte.
 12. The method according to claim 11, wherein said solidelectrolyte is coated on a heating element.
 13. The method according toclaim 12, wherein said heating element is a filament.
 14. The methodaccording to claim 11, wherein a heating element is embedded in saidsolid electrolyte.
 15. The method according to claim 14, wherein saidheating element is a filament.
 16. The method according to claim 10,wherein said electrolyte is a salt.
 17. The method according to claim16, wherein said salt is coated on a heating element.
 18. The methodaccording to claim 17, wherein said heating element is a filament.
 19. Amethod for generating product ions from sample molecules in an ionmobility spectrometer, comprising the steps of:applying a sampleconsisting essentially of a salt to a filament; inserting said filamentwith said sample into a reaction region of said ion mobilityspectrometer; heating said filament to cause emission of product ions,the ions being characteristic of said sample; using an electric field toassist in the extraction of the product ions; whereby said step ofheating the filament produces said product ions independently of saidcarrier gas composition and without a need for hydrogen to catalyze saidemission of product ions; and submitting said product ions to a drifttube of said ion mobility spectrometer for separation of said productions which have different mobilities.